Ai-chan asked Tony about this about a year back, but Tony only said something along the line of "Sorry, Ai-chan." So yeah, if Tony is going to implement larger images, it would've happened by now. Ai-chan wouldn't say it wouldn't happen, but if it does happen, it would be because Tony changed his mind.
Probably has something to do with server space. If the cover uses full-length image size, the server would be filled up quickly as there would be thousands of HQ images. Some people don't have restrain and want to go full bombastic like how some amateur indie game programmers want to go full HD 3D games these days without considering performance or aesthetics. But if authors put it on their chapters, there would be no space used as you can't upload images in the chapters, you can only hotlink it.